Question

Question 4

You are now convinced that you know the cause of death for these victims and quickly report it back to the police
as this is a very dangerous situation. After realizing that the electron transport chain was no longer functioning, you
started to suspect poisoning and ran a blood test for various poisons that you knew affected the electron transport
chain. The test of all seven patients came back positive for cyanide. Cyanide irreversibly binds to cytochrome c oxidase
(CcOX) of the electron transport chain and prevents the transfer of electrons to oxygen, the final electron acceptor.

A. What effect would cyanide have on the electron transport chain and the production of ATP? Explain your
answer.
B. Given what you now know about the action of cyanide on cellular respiration, explain why the patients died of
lack of oxygen while their blood oxygen levels were normal?
C. Would artificial respiration or oxygenation have saved these people? Why or why not?
D. Looking back at the information you have about the people before they got sick, can you suggest a possible
source of the cyanide poisoning? How should public health officials and police respond to this tragedy?

Answer 1

A. Cyanide binds reversibly with mitochondrial cytochrome oxidase a3 within the mitochondria. The latter is essential for the reduction of oxygen to water in the fourth complex of oxidative phosphorylation. As a result of which oxygen cannot bind to the fourth molecule in the ETC. The final reaction stops due to the inavailability of oxygen. The entire process of cellular respiration comes to a halt and thus no ATP is produced.

B. Even though the oxygen levels were normal, there was blockage of oxygen in the ETC. The patients did not die due to deprivation of oxygen, but due to the failure of the cells to use oxygen. The cells died due to the inability to use oxygen. Cyanide interfered with the process of cellular respiration.

C. Artificial respiration would have served the purpose because in this case the cells are dieing due to the inability of the cells to use the available oxygen. So oxygenation would be a better option because it would then readily provide the required oxygen to the cells.

D. There is no information mentioned here regarding how the people got sick and previous exposures to any food or external source. However, some natural occurrences of cyanide include seeds of apple, apricots, almonds etc. And cyanide can also be encountered to in enclosed space fires.

Public health officials should create an awareness regarding the avoiding the usage of the above mentioned fruit seeds and people should be asked to refrain themselves from closed spaces with fire. The fatal effects of cyanide should also be informed to the general people.